saving is a funny term really, it can be so fluid.
You will have your basics that don't really change much so write those down eg housing costs (fuel, water, mooring fee? laundry). Your typical food shop and so on.
Think about how much you spend over a year on clothes and shoes and again divide into a monthly figure.
and of course you need fripperies money for books, make up, magazines, takeaway, a night out etc.
You need contents insurance at the very least and should have some form of insurance on your boat. You should also look at low insurance just to cover funeral costs even though you have no dependents. Plus i assume you have car insurance, mot etc. many of these may be an annual cost and it tends to be cheaper to have it annual but still split it into monthly and put the amount away into a savings pot each month so you can pay as a lump sum and never get a nasty surprise.
It is also a good idea to put an amount towards the typical cost of your car service away each month plus some extra top build up a car replacement fund.
stuff like the car fund is then there and can, if the shit hits the fan, be used to live off.
We find a general savings pot makes us twitchy about spending so we split it and have amounts each month going into different pots for home repairs, holidays and so on plus a general savings pot. It means we can do work to the house when it needs it without seeing our main rainy day fund diminish but when you add the pots together we have a decent amount should we find ourselves in a tight spot.